Bottom bracket life?

dfz04

The internal screw thread on my bottom bracket (for the crank bolt) is completely stripped and useless. This has happened after less than a year of moderate (if frequent) riding on hard surfaces only. Is this to be expected through normal wear and tear or does it sound like a manufacturing defect?

nicklouse

Sounds like it has either been over tightened or has been ridden with a lose crank arm.

Threads do not wear.

What is the BB crankset?

dfz04

Not sure what type it is. If it was due to loose crank arm how long would it take for this damage to occur?

cooldad

Not long. A short ride with a loose crank will do it.

dfz04

Can the crank bolt loosen itself spontaneously?

cooldad

Any bolt can loosen. All fixings should be checked regularly.

nicklouse

Again what is the BB Crankset?

dfz04

nicklouse:
Unfortunately I can't check at this minute but froma quick google search I beleive it would be the same type as the guy in this thread: viewtopic.php?p=15437570

The information printed on my original BB is "CH52-68, 122L, BC1.37x24T", it is made by "CHIN HAUR" and it was standard on my carrera vulcan.

cooldad:
How often would you check the crank bolt though? After all if it was thread locked (as I expected it would be, though this doesn't appear to have been done) wouldn't you want to leave it alone to avoid very risk of accidentally loosening or over tightening it? Also, I have read that they are usually manufactured to be self tightening with the drection of the pedalling action, is this necessarily true (unfortunately I couldn't tell because there wasn't enough left of the thread!)

As you might have guessed, I'm trying to work out how much ground I have for claiming I was sold a defective item under the Sale of Goods Act, as they are refusing to honour the warranty and want to charge me for replacement parts and labour. pretty frustrating considering how long (or not really) I have had the bike.

supersonic

I check my bolts before every ride. And most manufacturers and manuals will have a time scale of checking stuff.

Square taper cranks need to be checked regularly, threadlocked or not. They are an interference fit onto the axle, and pedaling in this case does not tighten them (it is not like the pedals or bottom bracket cups). However over time the crank can move a little on the taper. This loosens the bolt.

I don't think you have any grounds if you have never checked the bolt. Almost all cases of cranks falling off and broken crank bolts are user error I am afraid.

cooldad

How often? Like the proverbial piece of string. Often enough. I have a square taper BB going on for 25 years old.
Unlike SS I'm lazy, so when I'm doing something to a bike, adjusting, fixing etc I just run over everything I can.